For electrolytes constituting electrochemical devices such as batteries, capacitors and sensors, liquid electrolytes have conventionally been used from the viewpoint of ionic conductivity. They had however problems such as fear of these devices being damaged by liquid leak.
In order to overcome such a problem, secondary batteries using a solid electrolyte such as inorganic crystalline material, inorganic glass or organic polymer have recently been proposed. Compared with the use of a conventional liquid electrolyte employing a carbonate solvent, use of such a solid electrolyte improves reliability and safety of the device because it is free from the leak problem of the carbonate solvent and enables reduction in ignition property to an electrolyte.
Since organic polymers usually have excellent workability and moldability or formability, can provide an electrolyte equipped with flexibility and bending property and heighten freedom of design of the device to which the resulting electrolyte is applied, they are expected as a promising material.
Polymer electrolytes obtained by incorporating a specific alkali metal salt in the organic polymers as described above, for example, polyethylene oxide however have an ionic conductivity lower than that of the liquid electrolytes and are therefore inferior thereto (for example, Z. Stoeva et al., J. Am. Chem. Soc. 125, 4619(2003)).
In addition, in the polymer electrolytes, the alkali metal salt incorporated therein dissociates into a cation portion and an anion portion and respective ions transfer, but their selectivity plays an important factor. In particular, when polymer electrolytes are applied to lithium ion batteries, a higher transference number of lithium ions is desired. Improvement in the transference number of lithium ions however decreases ionic conductivity, making it difficult to apply it to lithium ion batteries (for example, M. A. Mehta, et al., J. Power Sources, 81-82, 724(1999).
An object of the present invention is to provide an ionic-conductive polymer electrolyte satisfactory in both ionic conductivity and transference number of lithium ion and a novel polymerizable boric compound useful as a raw material for the ionic-conductive polymer electrolyte.